Dysfunction of the lower urinary tract and bowel systems affect nearly 100 million patients worldwide and, with a continued aging population, the incidence of these conditions will continue to grow. Medical science increasingly supports the primary theory for this dysfunction as an abnormal neurological communication between regulatory nervous system and the end organs (bladder, rectum, vagina, prostate etc. . . . ) being innervated. The regulatory nervous system, including the central nervous system (brain and spinal cord) and the peripheral nervous system, which system innervates the end organs and includes both afferent (sensory) and efferent (motor) divisions. Deterioration in the normal neuro-transmitted signals traveling up the afferent nerves carrying sensory feedback information as well as efferent motor axons signals traveling down the nerves toward their target tissues (most often muscle) can be precipitated by direct injury to the nerves, by an illness, or by aging. As a result, patients can develop various medical conditions to the end organs in the pelvis, i.e., the bladder and rectum, related to storage and elimination. Problems of storage as well as elimination of urine in the bladder can result in symptoms such as frequency, urgency (an overactive bladder), and incomplete bladder emptying. The rectum can have similar problems including fecal incontinence or chronic constipation.
Although first line therapies, such as diet or behavior therapy, and second line treatments, such as medications, can be helpful, many patients are simply non-compliant, see limited benefit, or suffer from intolerable side effects leading to discontinuation of their medical therapy. A third line therapy, neuromodulation, has been well-established as a safe and effective modality originally for refractory voiding dysfunctions and overactive bladder since 1997 and, more recently, since 2011, for fecal incontinence. Neuromodulation is the application of targeted electronic stimulus to modify primarily and directly afferent and efferent nerve signaling. Its direct application to the sacral and pudendal nerves in the pelvis and the posterior tibial nerves is quite effective for lower urinary tract and bowel dysfunction. Additional disorders involving the abdomen and pelvic organs, or muscle systems, such as Irritable Bowel Syndrome, interstitial cystitis, bowel motility disorders as well as chronic pelvic pain and sexual dysfunctions are being studied for potential benefit by neuromodulation. Neuromodulation has also been used safely and effectively to help relieve chronic back pain, pain from cancer and other nerve injuries, and pain from Complex Regional Pain Syndrome (CRPS) and Reflex Sympathetic Dystrophy (RSD), greatly improving the quality of life for patients. Presently, there are few treatments that can improve the activity level and the psychological outlook of a patient suffering from urinary or bowel dysfunction and/or pain disorders as well as neuromodulation techniques.
Neuromodulation presently involves a percutaneous procedure (although transvaginal or other natural orifice approaches are feasible) involving the placement of a needle to optimal proximity adjacent the desired nerve root, nerve, or branch, which then allows the physician to subsequently deliver a lead electrode introduced down the lumen of the needle. Proper or optimal positioning of the lead electrode within a very close proximity of the selected nerve is critical to achieve effective electrical stimulation, which promotes the desired clinical response. Currently, the delivery process is guided by fluoroscopic images of bony and soft tissue anatomical landmarks. Once fluoroscopic guidance has been achieved, electrical stimulation is employed to elicit motor and sensory responses from the patient to further refine or guide lead location.
Unfortunately there is a large margin of subjectivity to the interpretation of these “key” clinical responses. This includes both the patient's subjective assessment (i.e., feeling) and reporting (sensory response), and the implanting physician's subjective assessment when observing motor responses. Currently, physician measurement of response to neuromodulation stimulus is based on subjective markers such as a patient's perception of stimulation based on location of sensation and type of sensation. In the operating room, however, most patients are sedated or intubated. This leads to difficulty for patients to respond accurately to questions regarding sensation and location of stimulation. Not only does it require time for a patient to awaken to give feedback, medications adversely affect the patient's ability to respond accurately to questions, and there is a lack of clarity as to whether one's perception of appropriate stimulation is equated with actual stimulation efficacy. Objective measures of stimulation efficacy by the physician are based on a “bellows” response in the buttocks and dorsiflexion of the great toe. This, too, is open to subjective interpretation from the physician and it is unknown to what extent a patient may be able to exhibit these motor responses and the degree to which they need to be present to represent response.
As a result, despite what was thought at the time of implantation to be an optimal or “successful” lead placement, subsequent patient outcomes after lead deployment often does not correlate. In essence, with the current standard of care for performing neuromodulation, there is a poor correlation between the intra-operative method of evaluating electrode lead placement and postoperative optimal clinical success. The lack of consistent correlation between optimal intraoperative placement and postoperative clinical outcomes is an ongoing source of frustration for both patients and physicians. Suboptimal outcomes resulting in wasted healthcare dollars, despite what was thought to be a successful intraoperative placement, prevents a greater conversion of surgeons utilizing neuromodulation. A more specific and sensitive technique for optimal implantation would allow for greater postoperative patient success and ultimately greater acceptance and use among surgeons.
Compound muscle action potential (CMAP) or compound motor action potential is an electromyography investigation (i.e., an electrical study of muscle function). CMAP idealizes the summation of a group of almost simultaneous action potentials from several muscle fibers in the same area. These are usually evoked by stimulation of the motor nerve.
One common form of neuromodulation is referred to as InterStim therapy. Current forms of neuromodulation included sacral neuromodulation, pudendal neuromodulation, and posterior tibial nerve stimulation (Urgent PC).
Lower urinary tract complaints affect 1 in 3 adult women in the United States. Urinary urgency and urgency incontinence is a common form of urinary tract dysfunction. While not a cause of mortality, the morbidity of urinary urgency and urgency incontinence affects millions of women annually. Thirteen billion dollars was spent last year to control urinary incontinence. Many forms of therapy exist to help curb urinary urgency and incontinence. The American Urologic Association (AUA) has created an algorithm to manage these complaints. Simple cares are implemented initially including fluid management, avoidance of bladder irritants and urge suppression. If these fail, the next tier of treatment is medication. Two classes of medications are used, anti-muscarinics and beta-3 agonists. Approximately 60% of patients may respond to the above two levels of treatment. However, side effects and limited efficacy limit the use of medications and compliance limits behavioral therapy. Many studies reveal that less than 20% of patients continue medical treatment beyond a few months and as many as 50% discontinue after a single month. The AUA recognizes a third tier of treatment for refractory symptoms. This level of care offers three choices, sacral neuromodulation (InterStim therapy), posterior tibial nerve stimulation (Urgent PC), and intradetrusor botulinum toxin A (Botox). Of these options, sacral neuromodulation is the only therapy recommended, as opposed to offered.
Sacral neuromodulation was developed in the 1980's and ultimately received FDA approval in 1997 for urinary urgency and urgency incontinence and was approved for non-obstructive urinary retention shortly thereafter. Over 150,000 InterStim implants have been placed since its inception and the therapy is growing logarithmically at this time, with over 50% of all implants placed in the last five years. Studies as well as multiple peer reviewed articles have shown excellent long term success using InterStim therapy. Sixty-five percent (65%) of urge incontinent patients are >50% improved over five years and over 60% of urinary retention patients are improved over five years.
InterStim therapy is a minimally invasive procedure that places a small electrode percutaneously in close proximity to the third sacral nerve root. This nerve level provides 80% of autonomic control to the bladder. A small needle A is placed next to the nerve root with the assistance of fluoroscopy (x-ray), as shown in FIG. 12. Based on the image and motor response (movement of the buttocks and great toe), the lead is placed temporarily for a two-week trial. During this time, the patient maintains a journal to document objective response to the test and, then, a decision is made to implant the lead under the skin for long term use. At this time, a generator (battery similar to a pacemaker) is placed under the skin in the buttock to operate the device for approximately five years. Of patients who currently trials the therapy, only about 60% go on to permanent implant. This is primarily due to lack of efficacy. Most experts feel this lack of efficacy is due to suboptimal lead placement at the time of the therapy trial.
The greatest limitation to optimal initial lead placement is the poor correlation between anatomical landmarks and actual neurophysiologic function. It has been believed that, if one places a lead and obtains motor responses and sensory coupling, then the lead is delivering effective therapy. Yet there has been no way to determine whether actual nerve stimulation is occurring. This may represent the single greatest reason why what seems to be an appropriate test fails.
One of the reasons why so many tests fail is the fact that current systems do not provide feedback indicating correct placement. FIG. 13 is a graph of a prior art monitoring device showing an example of a CMAP waveform as viewed by surgeons in the current state of the art. The electronic tracing curves on the display represent various depolarization and repolarization sets of the nerve being modulated through the electrode of FIG. 12. Each of the two dots B on each tracer curve is a “tracer spike,” which is given off by the stimulating energy supplied to the nerve by the electrode lead of the neuromodulation device. Not only is it difficult to review the curves in real time, it is also difficult to determine the tracer spikes and, thereafter, to determine if the CMAP result is optimal, thus indicating optimal lead placement. As is apparent, the display screen of the prior art shown in FIG. 13 includes the ever-present “clutter” of a typical “overbuilt” prior art system. Such prior art systems require each user to visually interpret the series of electrical signals and make a subjective overall impression of what represents a true nerve response and, in doing so, attempt to determine if the signals displayed show that true nerve response or electrical interference or a signal artifact. It takes significant time and experience on the part of the user to “ferret out” such differences and, even with experience, there still exist areas of debate and judgment for each patient and each procedure. These disparities lead to variations in potential effectiveness of each surgery.
With traditional EMG devices, one will either use their own professional judgment or rely on a technologist for interpretation. The need for additional trained personnel limits the potential adaptation and widespread use of this prior art technology.
It would be beneficial if this problem could be overcome successfully, thus leading to a much higher implant rate and patient success. Based on theoretical models, a much higher rate of patients may be responders to InterStim therapy if the lead placement could be improved. This is also a great hindrance to both novice and experienced physicians using InterStim therapy.
In other areas of medicine and surgery, monitoring of nerve function is commonplace. Nerve conduction studies are invaluable to diagnose and treat many neurologic conditions. Intraoperative nerve conduction studies are the standard of care with most back and neck surgeries to determine if a nerve is compromised. From the experience of these fields, there is emerging data indicating that the technology can be very useful in optimizing InterStim therapy.
It would be beneficial to have objective measures for stimulation efficacy and accuracy that will lead to more uniform patient response to neuromodulation therapy. This could result in a greater number of patients responding to test therapy. Also, it would be beneficial to have greater device longevity from lower operational voltages. With such features, patient symptom resolution and satisfaction will increase. Lack of ongoing efficacy could be assessed and triaged, thus leading to more accurate and less frequent reprogramming and direct lead replacement when needed. This will lead to more uniform algorithms for programming and better assess when a replacement lead is needed.
Thus, a need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.